Biochar stability and characterisation

Samenvatting

“Biochar” is a special form of charred organic matter (similar to charcoal) that is intentionally blended into soils to improve soil structure and fertility. As a material, biochar is the darkened, highly porous, carbon-ich, amorphous solid that is produced from pyrolysing biomass feedstock at temperatures between approximately 400 and 700 °C (Figure 1). Incorporating biochar into soil improves soil properties like water holding capacity and nutrient retention, which ultimately results in increased agricultural yields.

While biochar can be (co-)produced in many biomass thermochemical conversion pathways, slow-pyrolysis is presently the preferred technique for controlled production with the highest product yields.

Biochar can be produced from almost any organic matter, including waste materials, but lignocellulosic plant feedstocks are commonly used due to their abundance.

Biochar also represents a novel approach to atmospheric carbon sequestration: Unlike in the biomass from which it is produced, the carbon that is contained in biochar is extremely resistant to decay. In this way, the carbon contained in biomass which was initially removed from the atmosphere during photosynthesis will finally become stored in the soil as biochar instead of being rapidly cycled back to the atmosphere through decomposition (Figure 2). Biochar is thus a technology that can help mitigate climate-change, while simultaneously improving agricultural productivity and enhancing bioenergy schemes.

Schematic diagram of the biochar carbon storage pathway

The research explores two aspects of biochar: i) Determining the long-term stability of biochar in soil. ii) Developing biochar characterisation techniques to quantify its relevant properties and behaviours in soil.

With regard to biochar stability, the research aims to use in-situ isotopic techniques to definitively answer how much biochar-carbon remains stable in the soil and for exactly how long. This information is fundamental for the successful development of biochar as a carbon sequestration technology.

Concerning biochar characterisation, we are interested in formulating new analytic approaches to relate observed behaviours of biochar in soil to inherent material properties. In the first instance this will be to devise proxy assays and characteristics for long-term biochar stability. Further research will examine biochar surface chemistry for properties that relate to its nutrient and water sorption behaviour in soil.